Magnetic unit



H. R. WARNKE May 3, 1938.

MAGNETI C UNI T Filed Mar'ch 4, 1956 2 Sheets-Sheet 1 m? mm m wa w 1W A m MM 8 0 M w w "May 3, 1938. H. R. YWARNKE MAGNETIC UNIT 2 Sheets-Sheet 2 Filed March 4, 1936 INVENTOR. fi'reriff. Wizrmfl' BY&A-7IIMIW xii;

442 ATTORNEY.

Patented May 3, 1938 UNITED STATES PATENT OFFICE 2.115.195 MAGNETIC UNrr Herbert R. Warnke, New York, N. Y., assignor to Control Instrument-Company, Inc., Brook- 1711, N. Y., a corporation of New York Application March 4, 1936, Serial No. 67,025

1 Claim. (Cl. 179-117) The present invention comprises a magnetic openings provided in the ends of the permanent unit or element. This element is especially magnets. The permanent magnets are arranged adapted for sound apparatus such as microwith similar magnetic'pcles in contact with the phones or loud speakers. top plate and with opposite magnetic poles in The present invention relates to a very powercontact with the base plate so that the top plate 5 ful permanent magnet element adapted to coopbecomes one magnetic pole and the central pole erate with a movable member arranged in a piece becomes the other magnetic pole. narrow air gap between the terminal poles of A suitable carrier for a portion of an electrical the element. This movable member is connected circuitis mounted to oscillate in the narrow air in an electrical circuit in such manner that a gap between the terminal magnetic poles. In the 10 movement of the member, as in the case of a preferred form, this member comprises a voice microphone, induces an electrical current in the coil mounted upon a. diaphragm. This voice coil member; or where-the member carries a variable is connected with suitable electrical apparatus electrical current, as in the case of a loud as is well known in the art. When the diaspeaker, the reaction between the element and phra m is vibrated by sound waves, a variable 15 the member produces movement of the member. current is established in the voice coil and the The principal feature of the device is a condevice operates as a microphone. Where the structlon wherein the permanent magnets exert voice coil is energized by an electrical current a coercive force of a very high number of gilcorresponding to a sound wave, thevariable curberts; and since the magnetic circuit is capable rent causes the voice coil to oscillate in the air p of a' high degree of saturation and its reluctgap and to impart movement to sound amplifyance' is low a field of very 'many gausses is pro- 1 18 pp ratus, which may comprise a cone or duced in the narrow air gap between the poles. other vibrating device utilized for transforming The permanent magnets used in the device are movement into sound waves, as is well known in cast masses of magnetic steel, comprising nickel, the art. 1

cobalt, aluminum. and steel. The permanent Other features of the invention will be pointed magnets arepreferably formed of a barrel shaped out hereinafter by reference to the accompanyconstruction which provides a large central poring drawings forming a part of the specification tion adapted to carry magnetic lines of force to and wherein like parts are indicated by like a maximum capacity of the mass of metal formcharacters throughout the several figures of the ing the magnets. The preferred construction of fl lsthe element comprises a soft iron top plate pro- It is to beunderstood that the disclosure herevided with a circular opening anda similar soft with is illustrative and is not to be considered iron base plate carrying a central pole piece also in the limiting sense since the invention may be or .soft iron. This pole piece extends into the m di d n constructions other than those sp opening 'in the top plate with a narrow tubular 01156811! illustrated and describedair gap between the upper end of the central Pig. 1 is a plan view of the preferred form of pole piece and the top plate. Barrel shaped perthe invention, showing the diap agm removed. manent magnets are mounted between the soft B- 2 1S Secflonal View Q line i 1 iron top plate and the soft ironbase .plate and showin th diap a m d vo il in posi- 40 the engaging surfaces between the ends of the o a d i se tionbarrel shaped magnetsand the top and bottom Fig. 3 IS a sectional View OH 11118 o i 4 plates are accurately ground plane surfaces to also showing the diaphragm and the voice coil in insure of intimate contact between the members. pe i D S The joint between the central pole piece and the Y Fi 4 illustrates a m ifica ion as to the num- 45 bottom plate is also a ground fit so that the lines of pe anen magnet po e Pieces o a unit of force are transmitted throughout the device mi ar t t at shown in 1 h h pwithout loss at the points of connection. Suittion that the number of permanent magnets is able connecting bolts of brass unite the top plate increased, that the base plate is round, and that and. the bottom plate to establish compressive the top plate has been removed. 5

' forces holding the permanent magnets in posi- Referring to Figs. 1, 2, and 3. the device comtion. In order to prevent movement of the magprises a top plate I, of soft iron, provided with nets on the respective bottom and top plates, a central opening 2. The top plate I, in the presmall ground" dowelsextend from shallow openferred form of the invention, carries a shouldered ings in the respective plates into similar small bras ring 4 comprising a seat or holder for a suitable diaphragm. This brass ring 4 may be secured to the top plate i in any suitable manner as for example by brass machinescrews 5.

This brass ring has a screw threaded shoulder into which a brass clamp ring 8 is threaded in order to clamp the edges of a diaphragm I. In the preferred form of the device, the diaphragm 1 is provided with a mounting 8 that carries a voice coil 9 that extends into the opening 2 in the center plate. The top plate i is also provided with lugs l8 having mounting openings II for mounting the unit in any desired manner. The under surface i2 of the top plate is ground to a plane surface and a plurality of permanent magnets i l have their ends l5 also ground to plane surfaces in order that an intimate contact may be formed between the permanent magnets l4 and the top plate I. These permanent magnets |4 are also carefully ground to a common length. The ends of the permanent magnets ll are recessed to receive dowel pins it which set in shallow recesses in the top plate I. These dowel pins I6 prevent displacement of the permanent magnets I4 on the top plate I.

A bottom plate also of soft iron, is provided with a ground plane surface l8 which contacts with ground surfaces I! on the ends of the permanent magnets I4. Dowel pins 20 are recessed intothe lower ends of the permanent magnets l4 and into the bottom plate I! to position the permanent magnets l4 relative to the bottom plate IT. This bottom plate carries a soft iron cylindrical pole piece 2|, the base of which is ground to a plane surface 22 in order to form an intimate contact with the plane surface |8 on the bottom plate Preferably, the cylindrical pole piece 2| is formedwith an integral stub bolt section 24 which is threaded on the portion extending beyond the bottom plate I1 and carries a nut 25.

Preferably, the upper end of the cylindrical pole piece 2| has a portion 26 reduced in diameter to extend into the-centralopening 2 in the top plate and to provide a narrow tubular air gap 21 between the upper end of the cylindrical pole piece 2| and the side walls of the central opening 2. The top plate I, the bottom plate H, the central pole piece 2|, and the nut 25 are all preferably constructed from soft commercially pure iron in order to form efficient paths for magnetic forces originating with the permanent magnets A brass ring or collar 28 is attached to the under portion of the top plate I by suitable screws (not shown) or otherwise, and extends downward to enclose a portion of the cylindrical pole piece 2|- in order to accurately center the reduced portion 26 in the central opening 2 of the top plate to providethe uniform air gap 21. Bolts 29, preferably of brass, are secured to the top plate and pass through openings in the bottom plate il so that nuts 30 may be utilized to place the bolts 29 under tension to tightly clamp the permanent magnet l4 between the top plate I and the bottom plate H.

The construction illustrated in Fig.4 is similar to the construction illustrated in Figs. 1 and 2 with the exception that the four permanent magnets l4 illustrated in Figs. 1 and 2 are replaced by six permanent magnets il in the modifled construction. The base plate 3| is circular in form instead of substantially rectangular as illustrated in Figs. 1, 2, and 3. The number of bolts 29 have been increased from four to stantially the same as the construction illus trated in Figs. 1, 2 and 3.

The permanent magnet members I4 are cast masses of special alloy, particularly adapted to constitute permanent magnets having a very high coercive force and preferably comprise an alloy ofnickel 8 to 15%, cobalt 2 to 5%, alumi-' num 10 to 20%, and the remainder steel.

The construction is such that after the parts have been all assembled, suitable electrical conductors may be positioned around the permanent magnet members so that an electrical current of very high magnetizing force may be applied to the conductors to permanently magnetize the magnets after the device has been completely assembled with the same magnetic poles of the several magnets all pointing in the same direction. This results in a construction which is substantially permanent in its magnetic characteristics and produces a construction wherein the gauss and gilbert-units are very high. The construction is such that the magnetic forces are concentrated in substantially parallel planes extending radially through the air gap 21 so that a concentrated field exists in the air gap. The lines of force in this field are cut by any movement of an electrical conductor vibrating in the field. Since the lines of force through the air gap originate from permanent magnets, the output of the device' is free from distortion due to variations in the magnetic field, and, therefore, extremely high fidelity of operation is obtained by the present construction.

The usual connections to the voice coil, or vibrating electrical conductor, have been omitted for the sake of clarity. Neither has'any amplifylng apparatus been shown or described. It is to be understood that all electrical. connections are to be made in accordance with the skill of the art and that the device herewith disclosed is to be used in electrical circuits well knownto' magnets'of greater cross-section in the middle portion than at the ends thereof and arranged symmetrically around and having the axes thereof parallel to the axis of said cylindrical core, said permanent bar magnets being of barrel shape and comprising supporting struts extending between said plates, theinner sides of saidplates being ground to substantial plane surfaces and the ends of said permanent barrel shaped magnets being also ground to substantially plane surfaces whereby the ends of said magnets and the inner sides ofsaid plates form ground fitted engagements to obtain intimate contact between the ends of said magnets and said plates; dowel pins extending intothe centers of the ends of said permanent magnets and into said plates to locate said magnets-on said plates; and adjustable nonmagnetic tension members comprising screw bolts extending between said plates to urge said plates toward each other and thereby clamp the magnets tightly between the plates.

HERBERT R. WARNKE. 

